The iris surrounds the dark, inner pupil region of an eye and extends concentrically to the white sclera of the eye.
A. K. Jain, A. Ross, and S. Prabhakar, “An introduction to biometric recognition,” IEEE Trans. Circuits Syst. Video Technol., vol. 14, 2004 discloses that the iris of the eye is a near-ideal biometric.
For the purposes of recognition, an image of an iris region is typically acquired in an imaging system that uses infra-red (IR) illumination to bring out the main features of an underlying iris pattern. An iris pattern is a gray-scale/luminance pattern evident within an iris region that can be processed to yield an iris code. The iris pattern can be defined in terms of polar coordinates and these are typically converted into rectangular coordinates prior to analysis to extract the underlying iris code.
Strong sunlight can affect the performance of iris recognition systems because of shadows on a subject's face and/or light patterns being reflected from the iris, causing a significant performance degradation.
Further, it is known that substitute images containing iris regions of a person to be recognized, such as images shown in pictures, artificial objects, or monitors, can be presented to an iris recognition system, instead of the person themselves, for fraudulent purposes—this is commonly referred to as spoofing.